arXiv subjects

J. E. Drut

Publications and source records attributed to J. E. Drut.

30 records · Page 2Linked to original sources

arXiv2016

Ground state of the two-dimensional attractive Fermi gas: essential properties from few- to many-body

We calculate the ground-state properties of unpolarized two-dimensional attractive fermions in the range from few to many particles. Using first-principles lattice Monte Carlo methods, we determine the ground-state energy, Tan's contact, momentum distribution, and single-particle correlation function. We investigate those properties for systems of $N=4,8,...,40$ particles and for a wide range of attractive couplings. As the attractive coupling is increased, the thermodynamic limit is reached at progressively lower $N$ due to the dominance of the two-body sector. At large momenta $k$, the momentum distribution displays the expected $k^{-4}$ behavior, but its onset shifts from $k \simeq 1.8 k^{}_F$ at weak coupling towards higher $k$ at strong coupling.

cond-mat.quant-gas↗

arXiv2016

Indirect exciton qubit manipulation via the optical Stark effect in quantum dot molecules

We propose a coherent control scheme based on the optical Stark effect in optically generated excitons in quantum dot molecules (QDMs). We show that, by the combined action of voltage bias detuning sweeps and Rosen-Zener pulsed interactions, it is possible to dynamically generate and modify an anticrossing gap that emerges between the dressed energy levels of long-lived, spatially indirect excitons. We perform numerical and analytic non-perturbative calculations based on the Bloch-Feshbach formalism, which demonstrate that this effect induces a mechanism of coherent population trapping of indirect excitons in QDMs. Our results show that it is possible to perform an all-optical implementation of indirect-excitonic qubit operations, such as the Pauli-X and Hadamard quantum gates, across two defined axis of the Bloch Sphere.

cond-mat.mes-hall↗

arXiv2015

Thermal equation of state of polarized fermions in one dimension via complex chemical potentials

We present a nonperturbative computation of the equation of state of polarized, attractively interacting, nonrelativistic fermions in one spatial dimension at finite temperature. We show results for the density, spin magnetization, magnetic susceptibility, and Tan's contact. We compare with the second-order virial expansion, a next-to-leading-order lattice perturbation theory calculation, and interpret our results in terms of pairing correlations. Our lattice Monte Carlo calculations implement an imaginary chemical potential difference to avoid the sign problem. The thermodynamic results on the imaginary side are analytically continued to obtain results on the real axis. We focus on an intermediate- to strong-coupling regime, and cover a wide range of temperatures and spin imbalances.

cond-mat.quant-gas↗

arXiv2015

Harmonically trapped fermions in two dimensions: ground-state energy and contact of SU(2) and SU(4) systems via nonuniform lattice Monte Carlo

We study harmonically trapped, unpolarized fermion systems with attractive interactions in two spatial dimensions with spin degeneracies Nf = 2 and 4 and N/Nf = 1, 3, 5, and 7 particles per flavor. We carry out our calculations using our recently proposed quantum Monte Carlo method on a nonuniform lattice. We report on the ground-state energy and contact for a range of couplings, as determined by the binding energy of the two-body system, and show explicitly how the physics of the Nf-body sector dominates as the coupling is increased.

cond-mat.quant-gas↗

arXiv2015

Few-fermion systems in one dimension: Ground- and excited-state energies and contacts

Using the lattice Monte Carlo method, we compute the energy and Tan's contact in the ground state as well as the first excited state of few- to many-fermion systems in a one-dimensional periodic box. We focus on unpolarized systems of N=4,6,...,12 particles, with a zero-range interaction, and a wide range of attractive couplings. In addition, we provide extrapolations to the infinite-volume and thermodynamic limits.

cond-mat.quant-gas↗

arXiv2015

Energy, contact, and density profiles of one-dimensional fermions in a harmonic trap via non-uniform lattice Monte Carlo

We determine the ground-state energy and Tan's contact of attractively interacting few-fermion systems in a one-dimensional harmonic trap, for a range of couplings and particle numbers. Complementing those results, we show the corresponding density profiles. The calculations were performed with a new lattice Monte Carlo approach based on a non-uniform discretization of space, defined via Gauss-Hermite quadrature points and weights. This particular coordinate basis is natural for systems in harmonic traps, and can be generalized to traps of other shapes. In all cases, it yields a position-dependent coupling and a corresponding non-uniform Hubbard-Stratonovich transformation. The resulting path integral is performed with hybrid Monte Carlo as a proof of principle for calculations at finite temperature and in higher dimensions. We present results for N=4,...,20 particles (although the method can be extended beyond that) to cover the range from few- to many-particle systems. This method is also exact up to statistical and systematic uncertainties, which we account for -- and thus also represents the first ab initio calculation of this system, providing a benchmark for other methods and a prediction for ultracold-atom experiments.

cond-mat.quant-gas↗

arXiv2015

Pressure, compressibility, and contact of the two-dimensional attractive Fermi gas

Using ab initio lattice methods, we calculate the finite temperature thermodynamics of homogeneous two-dimensional spin-1/2 fermions with attractive short-range interactions. We present results for the density, pressure, compressibility, and quantum anomaly (i.e. Tan's contact) for a wide range of temperatures and coupling strengths, focusing on the unpolarized case. Within our statistical and systematic uncertainties, our prediction for the density equation of state differs quantitatively from the prediction by Luttinger-Ward theory in the strongly coupled region of parameter space, but otherwise agrees well with it. We also compare our calculations with the second- and third-order virial expansion, with which they are in excellent agreement in the low-fugacity regime.

cond-mat.quant-gas↗

arXiv2015

Universality in one-dimensional fermions at finite temperature: Density, pressure, compressibility, and contact

We present finite-temperature, lattice Monte Carlo calculations of the particle number density, compressibility, pressure, and Tan's contact of an unpolarized system of short-range, attractively interacting spin-1/2 fermions in one spatial dimension, i.e., the Gaudin-Yang model. In addition, we compute the second-order virial coefficients for the pressure and the contact, both of which are in excellent agreement with the lattice results in the low-fugacity regime. Our calculations yield universal predictions for ultracold atomic systems with broad resonances in highly constrained traps. We cover a wide range of couplings and temperatures and find results that support the existence of a strong-coupling regime in which the thermodynamics of the system is markedly different from the noninteracting case. We compare and contrast our results with identical systems in higher dimensions.

cond-mat.quant-gas↗

arXiv2009

The Finite Temperature Pairing Gap of a Unitary Fermi Gas by Quantum Monte Carlo Calculations

We calculate the one-body temperature Green's (Matsubara) function of the unitary Fermi gas via Quantum Monte Carlo, and extract the spectral weight function $A(p,ω)$ using the methods of maximum entropy and singular value decomposition. From $A(p,ω)$ we determine the quasiparticle spectrum, which can be accurately parametrized by three functions of temperature: an effective mass $m^*$, a mean-field potential $U$, and a gap $Δ$. Below the critical temperature $T_c=0.15\varepsilon_F$ the results for $m^*$, $U$ and $Δ$ can be accurately reproduced using an independent quasiparticle model. We find evidence of a pseudogap in the fermionic excitation spectrum for temperatures up to {$T^*\approx 0.20\varepsilon_{F} > T_c$}.

cond-mat.stat-mech↗

arXiv2009

Toward ab initio density functional theory for nuclei

We survey approaches to nonrelativistic density functional theory (DFT) for nuclei using progress toward ab initio DFT for Coulomb systems as a guide. Ab initio DFT starts with a microscopic Hamiltonian and is naturally formulated using orbital-based functionals, which generalize the conventional local-density-plus-gradients form. The orbitals satisfy single-particle equations with multiplicative (local) potentials. The DFT functionals can be developed starting from internucleon forces using wave-function based methods or by Legendre transform via effective actions. We describe known and unresolved issues for applying these formulations to the nuclear many-body problem and discuss how ab initio approaches can help improve empirical energy density functionals.

nucl-th↗

arXiv2002

Competing interactions in the XYZ model

We study the interplay between a XY anisotropy $γ$, exchange modulations and an external magnetic field along the z direction in the XYZ chain using bosonization and Lanczos diagonalization techniques. We find an Ising critical line in the space of couplings which occur due to competing relevant perturbations which are present. More general situations are also discussed.

cond-mat.str-el↗

arXiv2002

Instabilities in Luttinger liquids

We discuss the appearance of magnetic and charge instabilities, named respectively metamagnetism (MM) and phase separation (PS), in systems which can be described by a perturbed Luttinger liquid. We argue that such instabilities can be associated with the vanishing of the effective Fermi velocity v, which in some cases coincides with a divergence of the effective Luttinger parameter K. We analyze in particular an XXZ chain with next-nearest-neighbor interactions in different limits where MM shows up and an extended Hubbard model where in turn, PS occurs. Qualitative agreement with previous studies is found.

cond-mat.str-el↗